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Deformations Resulting from Instability in Tunnels: A Structural Engineering Study
Mohanad Abdulrahman Omar Bakarman, Muhammed Ikhsan Setiawan, Adi Prawito Departement of Civil Engineering, Narotama University Surabaya, Indonesia [email protected], [email protected], [email protected]
Abstract
In this paper, I will discuss the issue of tunnel stability in general, and the problem of large deformation in particular. Tunnels and underground projects are often in a complex environment. Stability is one of the most important issues during tunnel construction. Significant deformation of underground structures has always been a threat to infrastructure integrity during tunnel construction. Controlling deformation may seem like a simple task, but it is actually challenging. Tunnels are important to provide great help economically and environmentally and also help facilitate the wheel of life, there will be what the engineers said and suggested before.
Keywords:
Deformation, Infrastructure, Instability, Structural Engineering, Tunnels
1. Introduction
Tunnels are engineering structures and it's a long passage that is created underground, usually through a hill or under the surface of the water. and it is considered the tunnels are very old. The Egyptians and Babylonians built a tunnel about 4,000 years ago. (A Balasubramanian, 2014) And in the seventeenth century, the Canal du Midi or by the name of Languedoc was the first of many main channel tunnels in France which in 1666-1681 were considered part of the First Channel, connecting the Atlantic Ocean and the Mediterranean an interesting tunnel was constructed at the time for the Alpine railway, the first of which was a tunnel that took 14 years to build. It began in 1857 and was completed in 1871. (Eichten, Lane, and Quigg 2006) And over the past two decades, there has been a significant increase in the number of tunnels around the world. This indicates that the tunnels will continue to increase in the coming years due to the increase in population mass and the possibility of opening underground cities and due to the development of infrastructure for economic growth and protection of the environment and landscape. and it's uses for transportation systems such as fresh water or sewage transportation systems or oil and gas transportation. Storage and storage systems, as well as oil storage, water storage and use in hydroelectric power stations, ores treatment plants, water treatment plants and pumping stations, etc... Tunnel construction is a very complex process and one of the most serious and challenging in the field of civil engineering. So safety should be in the first place and one of the main objectives of any construction project, especially the tunnel, should be given a high priority throughout the construction period.
2. Literature Review
1. Based on (Zhao et al. 2021) bilateral deep foundation pit excavation would cause the stress redistribution and large deformation of the adjacent tunnel, first the numerical calculation software Midas GTS/NX , then the results show that the tunnel deformation increased fluctuating, with the cumulative uplift and convergent deformation of about 26 mm and 16 mm, the cumulative change of the lining stress at DM16 section inside the foundation pit was 6.02% greater than that at DM30 section outside of the foundation pit, indicating the effectiveness of the reinforcement measures.
2. Based on (Bian et al. 2019) Comprehensive investigations have been undertaken combining engineering, laboratory, and microscopic analyses. Since the monitoring results show that there might be a close relationship between the large deformation phenomena and water infiltration into the tunnel the results from in situ geo stress tests indicate that as a result of high tectonic stress and low rock strength, the field of Huangjiazhai Tunnel is an extremely high geo stress area.
3. Based on (Hong-gang and Li-fang 2022) The point safety factor of the tunnel-landslide system's interface (slip surface) is defined as the ratio of the node's shear strength to the sliding force, based on a three- dimensional numerical computation. And using an oblique tunnel- landslide system along the BAOJI- LANZHOU Passenger Dedicated Line as the major study target. The conditions during excavation, the conditions after building, according to our findings, the interface's point safety factor can be used as a quantitative indicator of the tunnel-landslide system's stability.
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4. Based on (Zhang et al. 2020) In view of the large deformation of thin-layer soft rock we performed an experimental investigation on the mineral composition, physical characteristics, and uniaxial compressive strength of the surrounding rock of the tunnel using the 3DEC-Trigon discrete element numerical simulation method. The results show that the main factors influencing the deformation of a thin-layer slate tunnel joint inclination, buried depth, water absorption, and softening of the surrounding rock the maximum deformation of the surrounding rock is observed for a joint angle of 45°, at which the buried depth is directly proportional to the deformation and failure of the tunnel.
5. Based on (Huang et al. 2019) The pressure field distribution and deformation law must be known to ensure rational design and safe construction in large deformation tunnels of soft rock. Theoretical analysis, numerical simulation and field observation are used to investigate the surrounding rock stress and displacement condition the results showed that the deformation of the surrounding rocks and the extent of the plastic area could be effectively controlled by the short seat construction method the optimal seat length in the construction is 10 to 14 meters therefore, reasonable reserved deformation should be adopted to avoid secondary drilling expansion.
6. Based on (Kumar and Pratiher 2021) In the laboratory, single-tunnel and twin-tunnel small- scale rock models are created the findings of the tests reveal that rock strength, overburden pressure, and tunnel spacing all have an impact on the stability of underground constructions. When the strength characteristic of rock changes, the deformation value of unlined tunnels increases from 21.05 percent to 27.58 percent, while it decreases from 11 percent to 21.42 percent for lined tunnels. In the twin tunnel, the deformation value drops from 20% to 15.78% when the separation is increased.
7. Based on (Hu et al. 2022) This study establishes the improved Nishihara model for prediction of rock deformation surrounding the Dingxi Tunnel. And the conclusions are as follows: Model creation and theoretical derivation, Apply the form, Limitations of the model and prospecting.so the critical point for future research is to dig deep into the model and improve it through the combination of deep learning and other methods.
8. Based on (Shi et al. 2019) When the tunnel's burial depth varies from 1.5D to 2.5D, the surrounding rocks are most likely to undergo considerable deformation during tunnel construction, according to the findings (D is the tunnel excavation span). When the invasion thickness exceeds 60 percent of the tunnel height, tunnel deformation accelerates. The ratio of clay thickness to tunnel burial depth is another important metric that, if it surpasses 0.25, might result in significant tunnel deformation.
9. Based on (Zhang et al. 2020) Because of the difficulty of supporting the soft rock tunnel under high pressure has been used support system of NPR. And the results showed that after the NPR cable support produces a certain stress concentration within 12 meters in the surrounding rock circle, and the lateral stress distribution is the vertical is relatively similar. The circumferential stress of the surrounding rocks is greatly reduced, and the stress range is reduced by 10%.
10. Based on (Zhou et al. 2021) As the tunnel is excavated, the simulated displacement and stress using the bench approach increase abruptly the highest stress on the supporting structure is 18.13 MPa, and the maximum displacement is 45 mm, roughly twice the displacement The step technique's maximum settlement is 0.57 times that of the entire section, and the bench method's maximum stress is 0.39 times that of the CD approach as a result, the bench technique can better regulate the stability of the excavation face.
11. Based on (Wu et al. 2020) from a complete examination of the large deformation of the squeezing rock in the fracture zone two types of surrounding rock deformation control systems are proposed: "release while resisting," and "resistance combine release," respectively. "Strong support" and Scheme 1 (double initial support) Scheme No. 2 (single initial support). The results show that Scheme 2 outperforms Scheme 1 in terms of maximum deformation rate, maximum cumulative deformation, and monthly construction footage.
12. Based on (Xu et al. 2020) This study introduces a mobile tunnel (IMU), and Global Navigation Satellite System (GNSS) the system combines absolute measurement and relative measurement mode to judge the structural safety of tunnel section from multiple angles, high precision, and high efficiency.
13. Based on (Xue et al. 2018) Due to the special properties of loess, the deformation of tunnels constructed in loess is generally large and easily induced. To control deformation during construction, the degree of influence of multiple factors on tunnel deformation is analyzed by data mining and a deformation prediction model is established the influence degree of each factor is calculated through mining statistical data collected from the project. Results obtained via the prediction model are in good agreement with field observations.
14. Based on (Ma, Yang, and Liu 2021) The deformation and failure mechanism of the original support were studied in order to control in deformation the results indicated the curved- wall design is superior to the straight-wall design, and the combined support of the long and short walls is superior to the straight-wall design, short anchor bolts can also help control the surrounding rock's deformation
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15. Based on (Faraj, Sherwani, and Daraei 2019) Relative displacements and a strength factor (defined as a strength-to-stress ratio) were first obtained, the parameters were then plotted on a Cartesian coordinate plane. Finally, a criterion for tunnel deformation prediction was given utilizing the optimum regression line crossing across all sites the results suggest that the strength factor of 0.38 can be utilized to establish the boundary between squeezing and non- squeezing circumstances, as well as anticipate the tunnel's behavior and kind of failure.
16. Based on (Y. Liu, Qiu, and Duan 2022) The energy principle was used to design a series of EDs in this research. The mechanical qualities of each ED were tested in a compression test, and the ED's construction parameters were further adjusted. The AED-IO developed in this work results indicated the AED- deformation IO's capacity increased to 75.79 percent after optimization, while Peak and constant resistance were lowered to 10.50 Mpa and 2.94 Mpa, respectively the AED-IO improved construction safety while also lowering construction waste. Additionally, unnecessary costs were reduced.
17. Based on (Wang et al. 2019) Massive fissures in the surrounding rocks are created by large deformation of tunnels in long wall coal mines, for engineering applications, the proposed model was implemented in a finite difference software (FLAC3D). The suggested model is supported by the fact that the predicted surface convergence of the underground aperture fits the in-mine data. As a result, the proposed model can be used to assess an underground tunnel's safe margin when it's adjacent to a subsurface water-bearing deposit. It also offers information on the subsurface tube design, which prevents groundwater inrush from the nearby area.
18. Based on (Lueprasert et al. 2017) Using a series of three-dimensional elasto-plastic numerical analyses conducted to investigate the influences of an adjacent loaded pile on an existing tunnel for varying pile tip positions with respect to the tunnel and soil stratum, the proposed method can effectively capture the response of the deformed tunnel as a distorted ellipse shape. Investigation of the analysis results reveal the pile-soil-tunnel interaction mechanism behind the tunnel deformation behavior due to an adjacent loaded pile.
19. Based on (D. Y. Liu et al. 2017) the simulation capability of a finite element method (FEM) considering the small-strain characteristics of soil was verified using a case study, the results indicate that the deformation mode of the retaining structure has a significant influence on the deformation of certain tunnels.
20. Based on (Lai et al. 2020) The excavation stability of tunnel is a key problem in tunneling engineering a mechanical model is used to determine the boundary curve of the plastic zone and the principal stress distribution of the surrounding rock of a circular tunnel under non-tectonic stress, the results indicate that the stability of the surrounding rock of a circular tunnel can be improved by restraining the malignant extension of the plastic zone, improving the principal stress environment, and allowing uniform distribution of the plastic zone within the controllable range of the support system.
3. Research and Methodology
To make sure protection in construction, the deformation must be regular in the tunnel in loess, which exhibits properties different from those of rocks and the horizontal convergence (HC) and crown settlement (CS) are widely used to assess the stability of this " tunnel structural system ". Based on the statistical evaluation, and this study by ANOVA on the analysis for evaluation in depth effects. cover at the deformation of the rocks surrounding the loess tunnels, and thru regression evaluation the relationships among them had been presented to determine the depth threshold of the cover (CDT) in the tunnel, a statistical analysis method Because of the specificity of loess, the regularity of deformation in loess tunnels has different properties than that of rocky tunnels. There are four characteristics of deformation: scientific, timeliness, reliability and convenience. Sequential drilling (SEM) method has been widely applied to improve the stability for tunnel face, eg : lateral drift method (BSDM), bench pit (BEM), central diaphragm (CD), cross-diaphragm (CRD).
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Figure 1. Research and Methodologi
The depth of the cap is used to choose a method for calculating the pressure of the surrounding rocks, which is one of the factors affecting the deformation of the surrounding rocks. And after completing the calculation of the data according to the factors that cover depth and extent, and then the result is presented of the ANOVA. For CS, when the difference in cover depth was 10m and 32 m, the probability that the deformation was at the same level was P = 0.312 > 0.05 and F= 1.13 < F crit=4.96. At these cover depth levels, there was no significant difference in deformation. However, when the cover depth was at 32 m, 95 m, 110 m, and 175 m, and the probability that the deformation was at the same level was P ≤ 0.001 < 0.05 and F = 17.74 > F crit = 2.99. At these cover depth levels, there was significant difference in deformation. And based on BEM, only the statistical data, CS and HC, were analyzed, and the study showed that the deformation treatment is different between BEM and between CRD, CD, BSDM, etc. which has a temporary support wall.
Several steps of regression analysis:
1. The slope equation is initially set, according to the cover depth and deformation data.
2. Solutions for regression coefficient.
3. The correlation test is performed and the correlation coefficient is determined.
4. The regression equation and the specific conditions for determining the direction of deformation can be combined with the depth of the cap, and the confidence interval for the expected value can be calculated, after the relevant requirements are met.
And for HC, when the cover depth was at 32 m, 95 m, 110 m, and 175 m, the probability that the deformation was at the same level was P ≤ 0.001 < 0.05 and F= 34.63 > F crit= 3.03 At these cover depth levels, there was significant difference in deformation. When the cover depth was less than 32 m, the influence of the
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cover depth on the deformation was not significant. While the cover depth changed from 32 m to 175 m, the variation of the cover depth had a significant influence on the deformation.
4. Discussion
Based on the cover depth increased, the deformation increased in the deep tunnel, and the deformation had a linear function relationship with the cover depth. As cover depth increased, the gap between theoretical and regression curves narrowed, the function connection became more useful as a result. The difference between these two curves widened as the cover depth was reduced, and the function relationship between cover depth and deformation became obsolete. The findings supported the hypothesis that the deformation data from the shallow tunnel was random.
Based on the calculations and because loess is naturally strong, the vertical stress of surrounding rock in the shallow tunnel was less than in the deep one, and the vertical deformation was more than the horizontal. The soil pressure grew as the tunnel depth increased, and the original stress was eventually replaced by tectonic stress, resulting in a rise in horizontal and vertical deformations. Finally, vertical and horizontal deformations tended to be equal, while CS/HC tended to be constant.
5. Results
Although ANOVA indicated that the deformation of the rocks surrounding the loess tunnel was related to the depth of the cap, the scattering plot between the CS and the depth of the cap was shown at a distance of 15.2 m. It was found that the greater the depth of the cover, the higher the linear correlation coefficient was also 0.616 when taking into account the incorrect direction, and then the hypothesis H0: 1 = 0 was tested using the t- test. The results were t = 3.046 > t (0.05) = 2.365, with a P value of 0.019 = 0.05. At the 0.05 significance level, there were enough data to indicate that cover depth and CS have a linear relationship, and the dispersion area between HC and cover depth was 15.2 m. When the depth of the hood was raised, the HC also went up. The coefficient of linear correlation was 0.830 when considering the incorrect direction. The t-test was used to test the hypothesis H0: 1 = 0. The results were t = 9.5 > t (0.05) = 2.447 and P-value = 0.001 = 0.05. There was enough evidence at the 0.05 significance level to conclude that there is a linear relationship in the population between cover depth and HC and for further analysis of the relationship between deformation and cover depth, characteristics of the data on CS/HC from the site, using the SPSS software package, regression was performed Non-linear when the extension was 15.2 m, the depth of the cap ranged from 90 to 175 m, by comparing the graphs of (theoretical curve) and (regression curve). The difference between the two curves was significant when the depth of the cover was less than 90 meters. As cap depth increased, both curves followed the same pattern, with CS/HC gradually decreasing and stabilizing to a constant below sufficient depth. The CS depicts a scattering plot against the depth of the cap over a 12.26 meters range. Showed that as the depth of the cap grew, the CS also increased. The hypothesis H0: β1 = 0 was tested using a t- test. The results were the increase of ground pressure in the loess layer with the height of the cover depth as vertical breaks were generated, and the deformation after drilling increased proportionally, and the dispersal pattern between the HC and the cover depth was 15.2 m. As the depth of the cap grew, so did the HC. Given the linear trend, the linear correlation coefficient was 0.711 and after a t-test to test the hypothesis H0: β1 = 0. The results were t = 6.280 > t (0.05) = 3.365 and a P-value = 0.004 < 0.05 = a. At the 0.05 significance level, there were sufficient data to demonstrate a linear association between cover depth and HC. The slope for CS/HC and cover depth were then analyzed over 12.26 m. And CS/HC data are explored from the site, for further analysis of the relationship between deformation and cover depth. The CS/HC was varying with the depth of the cover when the extension was 12.26 m, the depth of the cover ranged from 45 to 100 m, by comparing the graphs it is seen as a theoretical curve, the other considered as a regression curve. The difference between the two curves was significant when the cap depth was less than 55 meters. However, with increasing cover depth, both curves followed the same pattern, with CS/HC decreasing and finally stabilizing at stabilization below sufficient depth, and at a distance of 12.26 m, comparison was made between the theoretical and regression curves of the CS/HC relationship with cover depth. All curves are represented with a graph.
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Figure 2. Histograms of tunnel deformation and normal distribution curve.
Regarding to the shallow tunnel, the tunneling deformation approached a normal distribution. The normal distribution was examined using the one-sample Kolmogorov-Smirnov test. And the results showed that in the shallow tunnels, the horizontal and vertical distortions were within 200 m.
6. Summary and Conclusion
Deformation most commonly occurs along the tunnel face during construction, shortly after progress, which makes it necessary to start monitoring deformation as soon as possible and allowable deformation of the rocks is necessary to avoid a second expansion of the excavation. The determination of the permissible deformation is based on obtaining the results of advanced geological prediction and observing the deformation of rocks. The hardness of the longitudinal steel arch is also effective in resisting large deformation, and the time factor is considered to have an effect on the tunnel deformation and stress concentration under the influence of external force and gradually causes the deformation of the rock mass and the tunnel. Over time, the deformation will increase and cause breakdown. In the loess tunnel the deformation must be uniform which shows properties different from those of the rocks and horizontal convergence (HC) and crown stability (CS) are widely used to assess the stability of this tunnel and there are four characteristics of the deformation: scientific, timeliness,
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reliability and comfort. When constructing the tunnel in Loess land, sequential drilling method (SEM) has been widely applied to improve the stability of tunnel face, lateral drift (BSDM), bench pit (BEM), central diaphragm (CD), cross diaphragm (CRD). The depth of the cap is used to choose a method for calculating the pressure of the surrounding rock, which is one of the factors affecting the deformation of the surrounding rock. When the difference in the depth of the cap was 10 m and 32 m, there was no significant difference in the deformation.
However, when the depth of the cap was 32 m, 95 m, 110 m, and 175 m, there was a significant difference in deformation. After analysis of variance (ANOVA) it was examined to study whether the tunnel deformation had a significant difference at several levels and at specific intervals. The results indicated that when the cap depth was less than 32m, the effect of cap depth on deformation was not significant. While the cap depth changed from 32 m to 175 m, the cap depth difference had a significant effect on the deformation. And regarding to the shallow tunnel, was using the Kolmogorov-Smirnov test. And the results showed that in the shallow tunnels, the horizontal and vertical distortions were within 200 m. As a result, a distortion allowance of 200 mm was advised.
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